1. Field of the Invention
The present invention relates to methods of making keyboard switches for use in pocket type electric calculators or the like.
2. Description of the Prior Arts
Hitherto keyboard switches for use in pocket type electric calculators or the like are formed as shown, for example, in FIG. 1. Switch keys 1 are disposed on one surface of a silicon rubber diaphragm 2. A moving contact 4, made of conductive rubber is fixed on the other surface of diaphram 2, underlying switch key 1. The moving contact 4 is moved downwardly by pressing key 1 and ultimately touches fixed contacts 5, 5' formed on a printed circuit board 3, thereby closing a circuit between the fixed contacts 5, 5'. The printed circuit board 3 has conductors on both surfaces thereof. A frame board 6, having through holes 61, is mounted on the silicon rubber diaphragm 2. Switch keys 1 are held in the through-holes 61. In order to prevent the switch keys 1 from passing out of through holes 61, each switch key has bottom collar 1a at the bottom thereof which engages the underside of associated top collars 62 in frame board 6. In order to assure enough mechanical strength, the bottom collars 1a should have thicknesses of at least 0.5 to 1.0 mm, and therefore, the overall thickness of the keyboard switch can not be drastically reduced. In order to reduce the thickness, it has been proposed, as shown in FIG. 2, to thin the bottom collar 1a by using keys 1 made of stainless steel and forming the thin collar 8b thereof by means of chemical etching. Alternatively, it has been proposed, as shown in FIG. 3, to make having an aluminum body 9 and stainless steel collar 10, about 0.1 mm thick, fixed thereto by calking. However, where a number of switch keys, e.g. fifty, are used in an apparatus, it is inconvenient and expensive to use keys such as shown in FIGS. 2 and 3. Furthermore, a printed circuit board 3 having conductors 5, 5" on both surfaces is rather expensive.